Each Seatrax pedestal crane is equipped with a patented mechanical anti-two blocking system to remedy offshore crane operations accidents caused by the unintentional contact between the hook block (or ball) and the boom point, often referred to as two-blocking. One type of two-blocking, often described as "booming down into the block," occurs on most cranes because of the location of the hoist drum, which is typically mounted on the revolving superstructure. Through this arrangement, the distance between the hoist drum and the boom tip sheaves increases as the boom is lowered, causing the lower block (hook block) to move closer to the upper block (boom tip sheaves).
Seatrax fixes this common problem by locating its hoist drums in the base section of the boom rather than the revolving superstructure. Through this arrangement, the hook block cannot be drawn into the boom tip sheaves as the boom is lowered. The hoist moves with the boom, allowing the distance between the hoist and the boom tip sheaves to remain unchanged.
With its basic design, Seatrax cranes require no external power source, switches, or valves, solutions other conventional cranes have used to combat two-blocking. Most often, crane manufacturers utilize a switch or valve, which interrupts power to the load hoist and/or the boom hoist and stops the offending motion. The switch is activated when the hook block approaches the boom tip sheaves and collides with a weight hanging from a rope or chain. This weight normally has a hole through which one of the lines to the hook block passes. When the block is hoisted to a predetermined position, it "lifts" the hanging weight and activates the switch or valve.
Two-blocking may also occur when crane operators over hoist the hook block (or auxiliary hook), regardless of the position or angle of the boom. Seatrax, through straightforward geometry, easily solves this problem.
For more information, read our technical paper on our anti-two-blocking system or call 713.896.6500.